[jdk20] RFR: 8298726: (fs) Change PollingWatchService to record last modified time as FileTime rather than milliseconds

[Tyler Steele]

This change fixes an issue with a jck test described in [JDK-8297275](https://bugs.openjdk.org/browse/JDK-8297275). The change applies cleanly.

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Commit messages:
 - Backport 5f63f7a742a1071a87ca69463bae6e04a44fe462

Changes: https://git.openjdk.org/jdk20/pull/64/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk20&pr=64&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298726
  Stats: 15 lines in 1 file changed: 2 ins; 4 del; 9 mod
  Patch: https://git.openjdk.org/jdk20/pull/64.diff
  Fetch: git fetch https://git.openjdk.org/jdk20 pull/64/head:pull/64

PR: https://git.openjdk.org/jdk20/pull/64